Astronomers Spot A Massive Black Hole That's Gone Rogue

Using the Chandra X-ray Observatory, astronomers have found evidence of a "wandering" black hole on the outskirts of a distant galaxy. It's too far away to cause us any trouble, but the discovery of this homeless ball of gravitational despair affirms a long standing theory about the existence of such objects. Image: Chandra X-ray Observatory

A massive black hole that's more than 100,000 times the mass of our sun has been detected in the outer regions of a galaxy located about 4.5 billion light years from Earth. Astronomers suspect that this "wandering" black hole was originally located at the core of a smaller galaxy, but it became dislodged during a merger with a larger one. Now homeless, it's settled into the outer reaches of the usurping galaxy.

Black holes — objects so heavy that not even light can escape them — come in a range of sizes. Stellar black holes measure about 16km across, and are up to 20 times heavier than our sun. Massive black holes, or so-called intermediate black holes, are 100 to 100,000 times heavier than our sun. At the top of the scale are supermassive black holes, which have upper masses ranging between 100,000 to 10 billion times that of our sun.

Both intermediate black holes and supermassive black holes are parked at the centre of their galaxies, but astronomers have theorised about the existence of "rogue" black holes — objects that have been jostled away from their galactic cores following a collision with a galaxy containing its own massive black hole. The stars, dust and gas from the second galaxy would disperse through the first one — along with its now displaced black hole.

Scientist have spotted a few black holes over the years that could qualify as wanderers, but nothing terribly compelling, and nothing quite on the scale of this latest discovery. Writing in the Astrophysical Journal, astronomer Dacheng Lin and colleagues describe a massive black hole that's located on the outskirts of a distant galaxy called GJ1417+52.

Image: Chandra X-ray Observatory

Black holes themselves may not be visible, but we can detect the damage they do in their immediate neighbourhoods. In this case, a star wandered too close to the rogue black hole, ripping it to shreds. The gaseous debris produced by this unfortunate encounter generated a tremendous amount of X-rays, which scientists on Earth were able to pick up using NASA's Chandra X-ray Observatory and ESA's XMM-Newton X-ray observatory.

The extreme brightness of this object classifies it as a "hyper-luminous X-ray source", and it features a mass about 100,000 times that of our sun. That's 10 times brighter than the brightest X-ray source ever seen for a candidate wandering black hole. Dubbed XJ1417+52, the object measures a whopping 3.13 million light years from tip to tip. The astronomers speculate that the black hole located within it originally belonged to a small galaxy that rammed into the larger GJ1417+52 galaxy.

At a distance of 4.5 billion years, this wandering black hole is nothing to worry about. But some scientists speculate that our very own Milky Way galaxy is home to hundreds of these massive objects, the remnants of early galaxy formation. None of these objects have ever been detected in our galaxy, but that doesn't mean they're not there. And even if they are, they're probably not as big as the unusually heavy GJ1417+52.

[Astrophysical Journal]

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